The present invention generally relates to geolocating a mobile unit from a single base station by relying on the repeatability of measurements made in the geographic operating area of the base station. More specifically, the invention is an infrastructure-based system and method, utilizing a base station having randomly located antennas, which uses a database of previously-determined ambiguous measurements, such as lines of bearing, serving base station pilot signal data for the sector in which the mobile unit is located as well as for the other sectors of the serving base station and neighbor base station pilot signal data, all of which are measured at the mobile unit from forward traffic channels (collectively, the serving base station pilot signal data and the neighbor pilot signal data are referred herein as the “pilot signal set”), and pilot finger data measured at the serving base station from the reverse traffic channel. This data is taken from a test unit at known locations throughout the geographic area served by the base station. The database is indexed with the known range and/or bearing from the base station to the test unit. The real-time ambiguous measurements are then compared with the reference ambiguous measurements in the database to thereby determine the geolocation of the mobile unit.
As used herein, the term “mobile unit” includes, but is not limited to, a mobile phone, tracking device, locating device, or any other wireless device that is in two-way communication with at least one base station. Examples of mobile units are mobile phones, vehicle location devices, fleet vehicle tracking devices, personal medical emergency transmitters, and other like devices. The term “infrastructure based” refers to systems and methods for geolocation where the measurements that are taken for geolocating the mobile unit are taken at the base station, switching office, or other typically non-mobile asset of the communication system. The term “randomly located antennas” refers to a group of antennas that are not in a predetermined pattern, such as an antenna array. The term “ambiguous measurements” refers to measurements whose values, either because of the method of obtaining the measurements or the nature of the measurements themselves, cannot be simply plugged into a mathematical equation to determine a unique geolocation. However, the ambiguous measurements are a function of the location of the transmitting device, either a mobile unit or a test unit, and are therefore repeatable. The present invention exploits the repeatability of the ambiguous measurements in order to obtain a geolocation estimate. The term “geomorphological data” includes, but is not limited to terrain features, buildings, road systems, etc. A “forward traffic channel” refers to communication signals being sent from a base station to a mobile unit while a “reverse traffic channel” refers to communication signals being sent from a mobile unit to a base station. The “serving base station” is the base station to which the mobile unit is sending its reverse traffic.
The term “pilot signal data” refers to data received at the mobile unit from the serving base station and neighboring base stations. As is know in the art, pilot signal data is unique for each base station, and each base station sector, and includes power level and timing information which the present invention exploits to determine a range from the mobile unit to the base stations as well as for defining a subregion of the serving base station's serving sector as will be described in detail below. The mobile unit scans for all detectable pilot signals as part of its normal operations. If the mobile unit detects a pilot signal from a neighboring base station, the mobile unit measures the power level and timing of the neighboring base station's pilot signal compared to the pilot signal of he serving base station.
The term “pilot finger data” refers to data derived from the set of correlators that try to despread communication traffic. The correlators are referred to in the art as “fingers”. The fingers can lock onto the direct path communication signal or multipath versions of the communication signal. A set of fingers are located at the mobile unit and at each base station. The data from the fingers includes received power and timing. The present invention uses the timing information at the serving base station in the calculation of range to the mobile unit as described further below. Current CDMA protocols may not allow for the transmission of pilot finger data from the mobile unit to the base station. However, the present invention contemplates the use of pilot finger data from the mobile unit in the determination of the geolocation of the mobile unit.
The present invention differs from other geolocation systems in one or more ways. Some prior art systems are mobile unit-based and determine the position of the mobile unit by receiving multiple dedicated location signals either from components outside the mobile unit's communication system, such as satellites and GPS systems or from a network of dedicated land-based antennas. Other prior art geolocation systems that are infrastructure-based use combinations of specific, as opposed to ambiguous, measurements generally from multiple base stations, such as angle of arrival, time of arrival, and time difference of arrival. These specific measurement values are used to solve a mathematical equation to determine the location of the mobile unit.
One prior art example of geolocation is based on time difference of arrival (“TDOA”) of radio signals at a plurality of base stations. Typical TDOA systems are described in U.S. Pat. No. 5,327,144 to Stilp, et al. and U.S. Pat. No. 5,317,323 to Kennedy, et al. for which the present inventor is a co-inventor. TDOA systems, such as the two previously mentioned and others, measure the time of arrival at a single antenna at a plurality of base stations of a radio signal emitted by a transmitter. The time of arrival is used to define sets of hyperbolic surfaces defining possible locations of the transmitter between each pair of base stations receiving the radio signal. The intersection of these hyperbolic surfaces define the location of the transmitter. The underlying technique of TDOA systems relies on geometric equations and the constant speed of the radio signal.
Another prior art example of geolocation is based on direction finding (“DF”) or lines of bearing (“LOB”). A typical LOB system is described in U.S. Pat. No. 4,728,959 to Maloney, et al. LOB systems determine the angle of arrival of the received wavefront of a radio signal emitted by a transmitter. The wavefront is received by an antenna array at a plurality of base stations. The antenna array must be of known dimensions, i.e., the distances between the antenna elements of the array must be known in order to determine the angle of arrival of the wavefront. The angle of arrival for each base station is determined by a radio wave phase difference at the antenna array as measured by the different antenna elements of the array thereby resulting in a line of bearing from the base station to the transmitter. The intersection of the lines of bearing from the plural base stations define the location of the transmitter. The underlying technique of LOB systems relies on geometric equations, the constant speed of the radio signal, and the relationship between the speed of the radio signal, the frequency of the radio signal, and the wavelength of the radio signal.
A third example of prior art geolocation is based on determining the distance of a transmitter from plural base stations. One method of obtaining the distance between a transmitter and a base station is two-way ranging. A typical two-way ranging system is described in U.S. Pat. No. 5,506,864 to Schilling. Two-way ranging entails sending a signal from a base station at a first known time to the transmitter, upon receipt of the signal the transmitter sends a signal back to the base station. The base station receives the transmitter's signal at a second known time, determines the difference between the first known time and the second known time, and calculates the distance between the base station and the transmitter. The result is a ring about the base station of possible locations for the transmitter. The intersection of rings from a number of base stations defines the location of the transmitter. The underlying technique of two-way ranging systems relies on the constant speed of the radio signals emitted by the base station and the transmitter. Some prior art systems use the same technique over time to determine successive loci of points in order to locate the transmitter.
A fourth prior art system uses signature matching to geolocate a mobile transmitter. One such system is described in U.S. Pat. No. 6,108,557 to Wax, et al. (“Wax”). The system described in Wax uses multipath signal signatures received at a base station from a transmitter and compares the received signal signature with a previously-determined set of reference signal signatures. Wax then performs several different specific mathematical matching techniques in order to determine the geolocation of the transmitter. The system and method described in Wax require, among other things, (1) that the base station have an antenna array of known dimensions, (2) specific mathematical matching techniques be used to determine geolocation from a set of possible geolocation solutions, and (3) only the signal envelope be present, i.e., the data contained in the signal is not a factor in determining the geolocation of the transmitter.
All of the above-described prior art systems rely on one or more of the following techniques and/or systems in order to geolocate a transmitter: taking measurements using calibrated antenna systems, using known geometric equations, specific mathematical pattern matching techniques to choose between possible geolocation solutions, and known physical laws. Additionally, all the above-described systems operate on the signal envelope, i.e., each prior art system only requires that a signal from the transmitter to be located be present and ignore the data that the signal carries. None of the prior art systems make use of the wealth of data carried by the signal. This wealth of data in the base station's and/or mobile unit's transmitter signals is useful in obtaining a more efficient and effective geolocation.
The present invention overcomes the deficiencies in the prior art by determining the geolocation of a mobile unit from a randomly-located group of antennas, such as the random grouping of antennas that might be found at a standard base station. An embodiment of the present invention uses the data contained in the signal from the mobile unit in order to determine the geolocation of the mobile unit. The present invention may also compare the time history of geolocation estimates to static information from maps and other geomorphological data to further refine the geolocation of the mobile unit.
Accordingly, it is an object of the present invention to obviate many of the above limitations in the prior art and to provide a novel system and method for geolocating a mobile unit from a single base station by relying on the repeatability of ambiguous measurements of the communication signals and pilot signal data transmitted by the mobile in the geographic area covered by the base station.
It is another object of the present invention to provide a novel system and method for geolocating a mobile unit from a single base station using an infrastructure-based system by comparing real-time measurements from the mobile unit which are a function of geographic position with a database of previously-received reference measurements.
It is yet another object of the present invention to provide a novel system and method for geolocating a mobile unit with a single base station having randomly located antennas where the system and/or method includes comparing real-time ambiguous lines of bearing with reference ambiguous lines of bearing.
It is still another object of the present invention to provide a novel system and method for geolocating a mobile unit with a single base station where the system and/or method includes comparing real-time pilot signal data with reference pilot signal data.
It is a further object of the present invention to provide a novel system and method for geolocating a mobile unit with a single base station where the system and/or method includes comparing real-time pilot finger data with reference pilot finger data.
It is yet a further object of the present invention to provide a novel system and method for geolocating a mobile unit with a single base station by performing a database search in order to match real-time ambiguous measurements with reference ambiguous measurements where the reference ambiguous measurements are indexed in the database by range and bearing from the base station.
It is still a further object of the present invention to provide a novel system and method for geolocating a mobile unit communicating with a single base station using a CDMA protocol.
It is an additional object of the present invention to provide a novel system and method for geolocating a mobile unit communicating with a single base station using a TDMA protocol. For TDMA air interfaces, pilot signal data and pilot finger data is composed of serving base station power and slot timing related information, and neighbor base station power and slot timing information.
It is yet an additional object of the present invention to provide a novel system and method for geolocating a mobile unit with an infrastructure-based location system at a base station where the antennas on the base station are not calibrated for direction-finding.
It is still an additional object of the present invention to provide a novel system and method for geolocating a mobile unit communicating with at least one base station using a communication protocol which requires spreading where the system and/or method includes the use of at least one of the number of signal elements being despread, the time delay between the receipt of direct path and multipath signals, and the power level of the mobile unit.
It is a further additional object of the present invention to provide a novel system and method for geolocating a mobile unit from at least one base station including estimating the geolocation of the mobile unit and comparing the estimated geolocation with static information to thereby refine the estimated geolocation of the mobile unit.
It is yet a further additional object of the present invention to provide a novel system and method for geolocating a mobile unit from a single base station by measuring certain parameters of the communication signal and pilot signal data of the mobile unit to thereby identify an ambiguous position estimate, compare the ambiguous position estimate with a database of reference ambiguous estimates to thereby determine the geolocation of the mobile unit without having to calculate the geolocation from a mathematical expression containing the measured parameters.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.